Information storage in HDD systems is arranged in concentric "tracks" upon the disks such that information density increases when the concentric tracks are placed closer together. The conventional parameter used to describe this characteristic is "tracks-per-inch" (TPI) which refers to the number of tracks measured along the radius of the disk.
The above referenced micro-actuator applications, and other prior art micro-actuator and multi-actuator designs have sought to enable more precise control of the position of the HDD read/write heads relative to a desired location, so that higher TPIs can be achieved in practical HDD systems compared to conventional single actuator HDD systems.
In the first co-assigned case cited above, an improved HDD actuator is described which overcomes limitations with rotation bearings, external disturbances, servo write errors, and mechanical resonance effects to enable HDD systems to operate with increased TPI disks using a translational micro-actuator. The micro-actuator design includes attaching a read/write head onto a translational micro-actuator installed at the end of the existing actuator arm; the micro-actuator can be precisely driven in position so that the read/write head can be adjusted, over a small range, from track to track.
The second co-assigned case cited above describes some techniques for sensing the position of the head carried by the micro-actuator. These techniques depend on measuring changes in physical quantities related to the micro-actuator position. These techniques rely on very small changes in physical properties and are sensitive to parameter variations.